High-entropy alloy and method for manufacturing same

ABSTRACT

A high-entropy alloy according to the present embodiment is a high-entropy alloy having an iron-rich phase and a copper-rich phase, and comprises a common complete solid solution metal that is completely solid-solved in iron and copper respectively. For example, the common complete solid solution metal may comprise nickel.

BACKGROUND Field of the Invention

The present disclosure relates to a high-entropy alloy and a method formanufacturing the same and, more particularly, to a high-entropy alloyand a method for manufacturing the same, which are improved incomposition and process.

Related Art

With the development of various industries, the development of materialsthat may simultaneously exhibit opposite properties beyond theproperties of a single material is required. In addition, due toregulations for protecting environment, it is required to reduce theweight of materials so as to improve the fuel efficiency of automobiles,the efficiency of electronic equipment, etc.

For example, in order to manufacture micro-parts with high strength andwear resistance, a high-entropy alloy with high fluidity andwettability, while simultaneously realizing opposite characteristics,i.e., excellent processability and strength, has been developed. Ingeneral, the high-entropy alloy is an alloy having a single-phasestructure of a face-centered cubic structure (FCC) or a body-centeredcubic structure (BCC) having a high mixed entropy by containing aplurality of elements in a predetermined amount or more.

However, the conventional high-entropy alloy is vulnerable to galvaniccorrosion due to a difference in potential and a difference in meltingpoint when different double phases are located in the same ratio,generates segregation during a casting process, or causes extraction orcracking of a low-temperature phase during a hot rolling process, sothat it is difficult to manufacture the alloy as a sheet material. Assuch, corrosion resistance is not excellent, and castability andprocessability are not excellent, so that it is difficult to manufacturemicro-parts.

SUMMARY

According to the present embodiment, there are provided a high-entropyalloy and a method for manufacturing the same, which have excellentcorrosion resistance, castability, and processability while havingexcellent strength and wear resistance.

In particular, there are provided a high-entropy alloy and a method formanufacturing the same, which can have various properties according to achange in composition, have excellent productivity, or be manufacturedby a simple manufacturing process.

A high-entropy alloy according to the present embodiment is an alloyhaving an iron-rich phase and a copper-rich phase, and includes a commoncomplete solid solution metal that is completely solid-solved in ironand copper respectively. For instance, the common complete solidsolution metal may include nickel (Ni).

The high-entropy alloy may further include a melting point loweringelement for lowering a melting point of the high-entropy alloy. Themelting point lowering element may include at least one of carbon (C),silicon (Si), phosphorus (P), and manganese (Mn). In addition, thehigh-entropy alloy may further include at least one of aluminum (Al),manganese (Mn), and chromium (Cr).

For example, the high-entropy alloy may include 15 to 80 at % iron, 1 to30 at % copper, 1 to 20 at % nickel, 5 to 20 at % aluminum, 0 to 20 at %manganese, 0 to 15 at % chromium, 0 to 5 at % carbon, 0 to 2 at %silicon, 0 to 2 at % phosphorus, and other unavoidable impurities.

The content of the copper in the iron-rich phase may range from 1 to 30at %.

The iron-rich phase may be contained in a larger volume ratio than thecopper-rich phase to be present as a main phase, and the copper-richphase may be partially present.

A method for manufacturing a high-entropy alloy according to anembodiment includes an iron melting step of melting an iron-containingmaterial including a melting point lowering element and iron to form amolten metal; a high melting point material melting step of putting ahigh melting point element that has a melting point higher than that ofthe iron-containing material into the molten metal, and melting the highmelting point element; a copper melting step of putting copper into themolten metal, and then melting the copper; and a low melting pointmaterial melting step of putting a low melting point material that has amelting point lower than that of the copper, and then melting the lowmelting point material.

The iron-containing material may include pig iron.

The melting point lowering element may include at least one of carbon,silicon, phosphorus, and manganese.

At least two of a first melting temperature of the iron melting step, asecond melting temperature of the high melting point material meltingstep, a third melting temperature of the copper melting step, and afourth melting temperature of the low melting point material meltingstep may have different temperatures. The second melting temperature maybe higher than the first melting temperature, the third meltingtemperature may be lower than the second melting temperature, and thefourth melting temperature may be lower than the third meltingtemperature.

The high-entropy alloy may include a common complete solid solutionmetal that is completely solid-solved in iron and copper respectively.Alternatively, the high melting point material may include at least oneof nickel and chromium.

The low melting point material may include aluminum. In the low meltingpoint material melting step, aluminum ingot may be pushed into a bottomportion of the molten metal to be melted.

A method for manufacturing a high-entropy alloy according to anotherembodiment a basic step of putting a plurality of materials includingiron, copper, and a common complete solid solution metal that iscompletely solid-solved in iron and copper respectively; a step offorming inert gas atmosphere after vacuum; and a melting step of meltingthe plurality of materials.

The plurality of materials may further include at least one of carbon,silicon, phosphorus, aluminum, manganese, and chromium, and the commoncomplete solid solution metal may include nickel.

The iron may include pig iron or pure iron.

According to the present embodiment, a high-entropy alloy having adouble phase structure, i.e., an iron-rich phase and a copper-rich phasemay include a common complete solid solution metal, thus reducing adifference in potential and a difference in melting point between theiron-rich phase and the copper-rich phase. This can prevent or minimizegalvanic corrosion, effectively prevent segregation from being formedduring casting, and prevent extraction or cracking of a low-temperaturephase from occurring during hot rolling. Thus, it is possible to improveall of strength, fluidity, wettability, corrosion resistance,processability, and castability. Further, a material cost can be reducedby reducing a relatively expensive copper content and increasing arelatively inexpensive iron content. In this case, it is possible tomanufacture a high-entropy alloy having various desired properties onlyby changing a composition, thereby improving productivity and quality.

In particular, because the high-entropy alloy according to the presentembodiment has excellent castability, a 2 mm mesh channel may be filled,so that it can be applied to a casting part that requiresminiaturization and weight reduction, and the degree of freedom indesign can be increased, thus improving a variety of performance. Such ahigh-entropy alloy can be melted and manufactured under atmosphericconditions by controlling an input sequence and a melting temperature,thus improving productivity, and can be melted and manufactured in aprocess using vacuum, thus simplifying a manufacturing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method of manufacturing ahigh-entropy alloy according to an embodiment of the present disclosure.

FIG. 2 is a flowchart illustrating a method of manufacturing ahigh-entropy alloy according to another embodiment of the presentdisclosure.

FIG. 3 is a field emission scanning electron microscope (FE-SEM)photograph of a high-entropy alloy according to an example 1.

FIG. 4 (a) to (c) are photographs in which a salt spray test isperformed on the high-entropy alloy according to the example 1.

FIG. 5 is a photograph in which a salt spray test is performed on ahigh-entropy alloy according to a comparative example 1.

FIG. 6 (a) and (b) are photographs in which a salt spray test isperformed on a high-entropy alloy according to an example 2.

FIG. 7 (a) and (b) are photographs in which a salt spray test isperformed on a high-entropy alloy according to an example 3.

FIG. 8 is a photograph of a sheet material that is formed by processingthe high-entropy alloy according to the example 1.

FIG. 9 is a photograph of an Oldham ring having the thickness of 1.7 mmmanufactured using the high-entropy alloy according to the example 1.

FIG. 10 (a) and (b) are photographs of the results of performing 2 mmmesh channel evaluation on high-entropy alloys according to examples 5and 6, respectively.

FIG. 11 is a photograph of the result of performing 2 mm mesh channelevaluation on cast iron according to a comparative example 4.

FIG. 12 (a) and (b) are photographs of the results of performingwear-resistance evaluation on the high-entropy alloys according to theexamples 5 and 6, respectively.

FIG. 13 (a) to (c) are photographs of the results of performingwear-resistance evaluation on cast iron or high-entropy alloy accordingto comparative examples 4, 5, and 6, respectively.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a high-entropy alloy and a method for manufacturing thesame according to an embodiment of the present disclosure will bedescribed in detail.

Herein, the high-entropy alloy is a term that is used to distinguish itfrom a low-entropy alloy, and may collectively refer to an alloy havingthe entropy of a certain level or higher. For example, herein, thehigh-entropy alloy may include an alloy that has the entropy of 1.5 R ormore and is generally referred to as a high-entropy alloy, as well as analloy that has the entropy of 1.0 R or more and is generally referred toas a medium-entropy alloy. That is, the high-entropy alloy according tothe present embodiment may have the entropy of 1.0 R or more.

The high-entropy alloy according to the present embodiment is ahigh-entropy alloy having an iron-rich phase and a copper-rich phase,and may include a common complete solid solution metal that iscompletely solid-solved in iron and copper, respectively, or forms acomplete solid solution with each of iron and copper. For example, thecommon complete solid solution metal may include nickel (Ni). Herein,the iron-rich phase may mean a phase having the highest iron content(e.g., at %) among a plurality of materials (e.g., elements)constituting the phase, and the copper-rich phase may mean a phasehaving the highest iron content (e.g., at %) among a plurality ofmaterials (e.g., elements) constituting the phase.

In order to improve various properties of the high-entropy alloy, thehigh-entropy alloy may further include at least one of aluminum,manganese, and chromium. In addition, the high-entropy alloy may furtherinclude a melting point lowering element (melting point loweringmaterial) for lowering the melting point of the high-entropy alloy, andthe melting point lowering element may include carbon, silicon,phosphorus, manganese, etc.

Since iron is inexpensive, has excellent strength and ductility, and isgreatly changed in strength and hardness depending on a phase structure,it may be easily adjusted so that the high-entropy alloy has desiredproperties. The copper is low in melting point, and is excellent inelectric conductivity and thermal conductivity. Further, the copper isnot mixed with iron and forms a double phase structure having theiron-rich phase and the copper-rich phase, so that it is suitable forforming the high-entropy alloy capable of improving both iron propertiesand copper properties.

Since the high-entropy alloy according to the present embodimentcontains iron an copper that are not mixed well with each other, theyare not mixed with each other unless other metals are contained, thusmaking it difficult to form the alloy. Thus, in order to prevent phaseseparation between iron and copper, the alloy may be formed to containaluminum, manganese, etc. having a predetermined solid solubility ineach of iron and copper. Accordingly, the high-entropy alloy has theiron-rich phase and the copper-rich phase, but may be changed in theratio of the iron-rich phase and the copper-rich phase depending on thecontents of iron and copper.

In the present embodiment, it may form a complete solid solution withiron, form a complete solid solution with copper having a high solidsolubility in iron, or include a common completely solid-solved metalhaving a high solid solubility in copper. For example, nickel that iscompletely solid-solved with copper, is completely solid-solved withiron with a high solid solubility, or has a high solid solubility may beused as a common complete solid solution metal. As such, if the commoncompletely solid-solved metal (e.g. nickel) is contained, this mayincrease the solid solubility of copper in the iron-rich phase in thehigh-entropy alloy having the double phase structure of the iron-richphase and the copper-rich phase, and increase the solid solubility ofiron in the copper-rich phase, thus reducing a difference in potentialand a difference in melting point between the iron-rich phase and thecopper-rich phase. Thereby, it is possible to prevent or minimizegalvanic corrosion that may be caused by the difference in potentialbetween the iron-rich phase and the copper-rich phase. Further, it ispossible to effectively prevent the formation of segregation that mayoccur during casting by a difference in melting point between theiron-rich phase and the copper-rich phase, and effectively prevent theextraction or cracking of the low-temperature phase during hot rolling.Thus, it is easy to perform casting or hot rolling. Moreover, nickel hasexcellent corrosion resistance, so that it is possible to improve thecorrosion resistance of the high-entropy alloy.

The inclusion of nickel may increase the solid solubility of copper inthe iron-rich phase, thus reducing a copper content throughout thehigh-entropy alloy. Thus, a material cost can be reduced by reducing thecontent of copper that is relatively expensive and increasing thecontent of iron that is relatively inexpensive. Further, it is possibleto lower a melting temperature and improve corrosion resistance in theprocess of manufacturing the high-entropy alloy.

In the present embodiment, the double phase structure including theiron-rich phase and the copper-rich phase may be obtained, and theirratios may not be equal. For example, the iron-rich phase is containedin a larger volume ratio than the copper-rich phase to be present as amain phase, and the copper-rich phase is partially present to preventthe formation of segregation, thus resulting in high strength,processability, castability, and wettability, and thereby causing thehigh-entropy alloy to have a uniform composition.

For example, the content of copper in the iron-rich phase may range from5 to 30 at % (e.g., 10 to 25 at %). This is set in consideration of thecontent of nickel contained in the high-entropy alloy, but the presentdisclosure may have various values without being limited thereto. Forreference, the content of copper in the iron-rich phase that does notinclude nickel may be less than 5 at % (e.g., 3 at % or less).

Further, aluminum is a lightweight element (lightweight material), andis mixed with iron as the low melting point element (low melting pointmaterial) to form a body-centered cubic structure. Aluminum may improvehardness, wear resistance, strength, etc. but may reduce ductility. Ifmanganese is contained in iron, this may improve both strength andductility. Further, manganese is lower in melting point than iron, andmay act as a type of melting point lowering element for lowering themelting point of the high-entropy alloy. Thus, the fluidity andcastability of the high-entropy alloy can be improved. When chromium isincluded in iron, a chromium oxide film may be formed on iron or theiron-rich phase to further improve corrosion resistance. Chromium may ormay not be included in the high-entropy alloy.

If the melting point is lowered by the melting point lowering elementsuch as carbon, silicon, phosphorus, or manganese, this has excellentfluidity and wettability and low high-temperature viscosity during themanufacturing process of the high-entropy alloy, thus improvingcastability. The melting temperature is low when a molten metal is made,so that it is possible to perform casting under atmospheric conditionseven if the low melting point material such as copper or aluminum iscontained. Thus, the quality of the high-entropy alloy can be improved.Here, when silicon is included as the low melting point element,castability can be improved and corrosion resistance can be improved byforming an oxide. When carbon is included as the low melting pointelement, the melting point can be effectively lowered. When phosphorusis included as the low melting point element, the melting point can beeffectively lowered even with a small amount of phosphorus.

For example, the high-entropy alloy may include 15 to 80 at % iron, 1 to30 at % copper, 1 to 20 at % nickel, 5 to 20 at % aluminum, 0 to 20 at %(e.g. 0.1 to 20 at %, e.g. 5 to 20 at %) manganese, 0 to 15 at % (e.g. 2to 15 at %) chromium, 0 to 5 at % (e.g., 3 to 5 at %) carbon, 0 to 2 at% silicon (e.g. 1 to 2 at %), 0 to 2 at % (e.g., 0 to 1 at %)phosphorus, other elements or unavoidable impurities.

To be more specific, if the content of iron is less than 15 at %,strength and ductility may be reduced. If the content of iron is morethan 80 at %, the contents of other metals may be reduced and thereby itmay be difficult to improve various properties in the high-entropyalloy. If the content of copper is less than 1 at %, the effects oflowering the melting point and improving the electric conductivity orthe thermal conductivity using copper may not be sufficient. If thecontent of copper is more than 30 at %, the contents of other metals maybe reduced and thereby it may be difficult to improve various propertiesin the high-entropy alloy.

If the content of nickel is less than 1 at %, the above-described effectmay not be sufficient by nickel. If the content of nickel is more than20 at %, the contents of iron and copper are not sufficient, so that itmay be difficult to improve various properties in the high-entropyalloy.

If the content of aluminum is less than 5 at %, the effect of aluminummay not be sufficient. If the content of aluminum is more than 20 at %,the contents of iron and copper are not sufficient, so that it may bedifficult to improve various properties in the high-entropy alloy andthe ductility of the high-entropy alloy may be reduced. Manganese may ormay not be included in the high-entropy alloy. When manganese isincluded in the high-entropy alloy, for instance, manganese may beincluded in the amount of 0.1 to 20 at % (e.g., 5 to 20 at %). This isto improve the effect of manganese while sufficiently maintaining thecontents of iron, copper, etc. Chromium may or may not be included inthe high-entropy alloy. When chromium is contained in the high-entropyalloy, for instance, chromium may be included in the amount of 2 at % to15 at %. This is to improve the effect of chromium while sufficientlymaintaining the contents of iron, copper, etc.

Further, if the content of silicon is more than 2 at %, a precipitatedphase may be formed in the high-entropy alloy, thus causing cracks in acast product. If silicon is included in the amount of 1 at % or more,the effect of silicon may be sufficiently realized. If the content ofcarbon is more than 5 at %, it may be difficult to sufficiently maintainthe contents of iron, copper, etc. and the melting point of thehigh-entropy alloy may be increased. When the high-entropy alloycontains carbon and the content of carbon ranges from 3 to 5 at %, themelting point may be effectively lowered. Further, phosphorus may beincluded in the amount of 2 at % or less so as not to significantlyaffect other properties while effectively lowering the melting point.

However, the present disclosure is not limited to the above-describedelements and contents. Therefore, the present disclosure may furtherinclude elements or materials as well as the above-described elements orcontents, and the content of each element or material may be variouslychanged in consideration of the desired properties of the high-entropyalloy.

The high-entropy alloy according to the present embodiment may be usedto manufacture various products. That is, the high-entropy alloyaccording to the present embodiment has both excellent fluidity andwettability due to copper, so that it is more excellent in castabilitythan cast iron, and thereby it may fill a 2 mm mesh channel. This may beapplied to a cast part requiring miniaturization. Further, a reductionin weight may be realized by thinly forming a part that requires areduction in weight. Furthermore, a variety of performance can beimproved by increasing the degree of freedom in design of a cast productdue to the casting possibility of a precise design. At this time, ahigh-entropy alloy having various desired properties can be manufacturedmerely by changing a composition.

For example, it is possible to manufacture an Oldham ring that preventsthe rotation of a scroll in a scroll compressor and enables only theleftward or rightward revolution of the scroll, using the high-entropyalloy according to the present embodiment. The weight reduction of theOldham ring is required to reduce noise and improve efficiency during anoperation. For example, the Oldham ring should be manufactured to havethe overall weight of 100 g or less, and a key part holding the scrollso as to be coupled with the scroll in the Oldham ring should beprecisely machined to have only the error of ±5 mm. As described above,the high-entropy alloy according to the present embodiment hascastability that may fill the 2 mm mesh channel, so that the Oldham ringhaving the thickness of 2 mm or less may be manufactured and a specificgravity may also be adjusted to 7.2 or less, thus providing a lighterweight compared to the Oldham ring made of general iron alloy.

An example of a method for manufacturing the above-describedhigh-entropy alloy will be described in detail with reference to FIG. 1. A detailed description of the same or similar parts to those of theabove description will be omitted and only different parts will bedescribed in detail. The above-described contents will be applied to thecontents of materials contained in the high-entropy alloy.

FIG. 1 is a flowchart illustrating a method of manufacturing ahigh-entropy alloy according to an embodiment of the present disclosure.

Referring to FIG. 1 , the manufacturing method of the high-entropy alloyaccording to the present embodiment may include an iron melting stepS10, a high melting point material melting step S12, a homogenizationstep S14, a copper melting step S16, a low melting point materialmelting step S18, and an impurity removal step S20. In the manufacturingmethod of the high-entropy alloy, it is possible to cast thehigh-entropy alloy under atmospheric pressure conditions (i.e. generalatmospheric pressure conditions, i.e. atmospheric conditions) other thana vacuum condition. This will be described in more detail.

First, in the iron melting step S10, a molten metal may be formed byintroducing an iron-containing material into molten metal manufacturingequipment and then melting the material. Various types of knownequipment may be used as the molten metal manufacturing equipment.

In the present embodiment, the iron-containing material may include ironand a melting point lowering element. For example, pig iron or pig ironand manganese may be used as the iron-containing material. Since the pigiron contains the melting point lowering element such as carbon,silicon, manganese, or phosphorus together with iron, the pig iron maybe used as it is and the melting point lowering element may beintroduced together. Here, the pig iron may include 5 at % (e.g. 3 to 5at %) carbon, and 1 to 2 at % silicon, manganese, phosphorus, or thelike.

In the iron melting step S10, the melting point lowering element may bemelted together with iron to lower the melting point of iron and therebyeffectively lower a first melting temperature. In particular, bybasically reducing the melting point of iron, it is possible to lowerthe fourth melting temperature in the low melting point material meltingstep S18 performed after adding the low melting point element, such asaluminum or copper, having a low melting point. Thus, in the low meltingpoint material melting step S18, it is possible to prevent aluminum orcopper from being oxidized at high temperature (e.g. 1600° C. or higher,i.e., more than 1520° C.). This will be described in more detail laterin the low melting point material melting step S18.

For example, the first melting temperature of the iron melting step S10may range from 1450 to 1520° C. In this temperature range, theiron-containing material can be stably melted and a burden in thehigh-temperature process can be reduced. However, the present disclosureis not limited thereto, and the melting temperature of the iron meltingstep S10 may be variously changed.

Subsequently, in the high melting point material melting step S12, thehigh melting point material having a melting point higher than that ofthe iron-containing material may be put into the molten metal to bemelted. The high melting point material may include a common completesolid solution metal that is completely solid-solved in iron and copperrespectively. For example, the common complete solid solution metal mayinclude nickel. Alternatively, the high melting point material mayfurther include chromium.

At this time, the second melting temperature of the high melting pointmaterial melting step S12 may be higher than the first meltingtemperature of the iron melting step S10. For example, the secondmelting temperature of the high melting point material melting step S12may range from 1650 to 1750° C. In this temperature range, a materialincluding chromium, nickel, etc. can be stably melted and a burdencaused by the high-temperature process can be reduced. However, thepresent disclosure is not limited thereto, and the second meltingtemperature of the high melting point material melting step S12 may bevariously changed.

Subsequently, the homogenization step S14 may be performed at ahomogenization temperature lower than the second melting temperature. Atthis time, in order to remove impurities, homogenization may beperformed by including flux. For example, the flux used to remove theimpurities may include Al₂O₃, CaO, SiO₂, etc. However, the presentdisclosure is not limited thereto, and the introduction of the flux, thematerial of the flux, etc. may be variously changed.

For example, the homogenization temperature of the homogenization stepS14 may range from 1450 to 1520° C. In this temperature range,homogenization and stabilization may be stably performed, and impuritiesmay be removed. The homogenization step S14 or the impurity removalprocess included therein may be performed for 1 minute to 10 minutes(e.g., 2 to 3 minutes). The impurities may be stably removed in thistime range, and it is possible to prevent productivity from beingdeteriorated due to excessively long process time. However, the presentdisclosure is not limited thereto, and the homogenization temperatureand/or the process time of the homogenization step S14 may be variouslychanged.

Subsequently, in the copper melting step S16, copper may be put into themolten metal to be melted.

The third melting temperature of the copper melting step S16 may beequal to or higher than the first melting temperature of the ironmelting step S10 and the uniformization temperature of thehomogenization step S14, and may be equal to or lower than the secondmelting temperature of the high melting point material melting step S12.For instance, the third melting temperature may be higher than the firstmelting temperature of the iron melting step S10 and the uniformizationtemperature of the homogenization step S14, and may be lower than thesecond melting temperature of the high melting point material meltingstep S12.

For example, the third melting temperature of the copper melting stepS16 may range from 1520 to 1650° C. The molten metal in the coppermelting step S16 contains a large amount of elements or materials havinga low melting point, including copper of a low melting point, to have arelatively melting point (i.e. melting point of 1150° C. or less, suchas 900° C. to 1100° C.). If the third melting temperature is defined asdescribed above in consideration of the melting efficiency along withthe melting point, copper may be stably melted after the copper isadded, and a burden in the high-temperature process may be reduced.However, the present disclosure is not limited thereto and the meltingtemperature of the copper melting step S16 may be variously changed.

Subsequently, in the low melting point material melting step S18, thelow melting point material having the melting point lower than that ofiron or the iron-containing material may be put into the molten metal tobe melted. The low melting point material may include aluminum or thelike. Here, aluminum may be pushed in the form of an ingot into a bottomportion of the molten metal, and then be melted or dissolved. Thereby,it is possible to minimize or prevent aluminum oxide formed by oxidizingaluminum from floating on a surface of the molten metal.

At this time, the fourth melting temperature of the low melting pointmaterial melting step S18 may be equal to or higher than the temperatureof the copper melting step S16. For example, the fourth meltingtemperature of the low melting point material melting step S18 may belower than the temperature of the copper melting step S16. This is tominimize a problem such as the oxidization of the low melting pointmaterial. For instance, the fourth melting temperature of the lowmelting point material melting step S18 may be 1500° C. or less (e.g.,1200 to 1400° C.). If the fourth melting temperature is more than 1500°C. (e.g., 1400° C.), aluminum is melted and simultaneously oxidized toform slag composed of aluminum oxide over the molten metal. Thus, aprocess of removing the slag should be added. If the fourth meltingtemperature is 1200° C. or less, a homogeneous molten metal may not beformed. However, the present disclosure is not limited thereto and themelting temperature of the low melting point material melting step S18may be variously changed.

Subsequently, in the impurity removal step S20, impurities (e.g. oxide,slag or the like present on the surface of the molten metal) may beremoved using the flux. The flux used for removing the impurities mayinclude Al₂O₃, CaO, SiO₂, etc. However, the present disclosure is notlimited thereto. Therefore, the impurity removal step S20 may not beperformed, and the introduction of the flux, the material of the flux,etc. may be variously changed in the impurity removal step S20.

A final molten metal from which impurities are removed may be tapped ata predetermined tapping temperature (e.g., 1400 to 1600° C., such as1500° C.), and be processed to have a desired shape (e.g., casting usinga mold having a desired shape). However, the present disclosure is notlimited thereto, and the tapping temperature or the like may bevariously changed.

In the manufacturing method of the high-entropy alloy according to thepresent embodiment, it is possible to perform processing or castingunder atmospheric pressure conditions (i.e. general atmospheric pressureconditions) other than the vacuum condition, thereby reducingmanufacturing costs, and allowing various parts of a desired shape to bemanufactured. In particular, pig iron with low purity may be used andimpurities may be easily removed, so that the quality of themanufactured high-entropy alloy may be excellent. Further, since thereis no limitation on the number of molds, the final molten metal may besequentially poured into the prepared molds to manufacture a largenumber of cast products together, thereby reducing costs.

In contrast, in casting using a vacuum process, it may be difficult topour the molten metal into the mold after manufacturing the final moltenmetal, and it may be difficult to reduce the manufacturing cost.Further, it may be relatively disadvantageous in terms of process timeand cost, and if a high-purity material is not used, it may be difficultto remove impurities in the final molten metal, so the quality of thefinished high-entropy alloy may be low. Further, since the number ofmolds that may be put into the vacuum chamber is limited, it isdifficult to manufacture a cast product, and a device capable of pickingthe molten metal out of the vacuum chamber should be prepared in orderto inject the final molten metal into the external mold. Accordingly,there may be difficulties in the process and an increase in cost.

Further, in the manufacturing method of the high-entropy alloy accordingto the present embodiment, at least two of the first to fourth meltingtemperature are different from each other. That is, in the presentembodiment, the molten metal may be manufactured by adjusting the inputsequence and the melting temperature in consideration of differentmelting points of a plurality of materials or elements contained in thehigh-entropy alloy, thus allowing the high-entropy alloy to have auniform composition, preventing cracks from occurring, and therebyimproving a quality. In contrast, in conventional atmospheric castingwithout controlling the pouring sequence and melting temperature,oxidation of a low melting point element (e.g. aluminum) occurs duringmolten metal production, resulting in non-uniform composition, orcracking due to ingress of oxide when pouring molten metal into themold.

Since the high-entropy alloy according to the present embodiment hasexcellent fluidity and wettability by including the melting pointlowering element, it may be stably injected into the mold merely bymaintaining a temperature level of about 1400° C.

Another example of a method for manufacturing the above-describedhigh-entropy alloy will be described in detail with reference to FIG. 2. A detailed description of the same or similar parts to those of theabove description will be omitted and only different parts will bedescribed in detail.

FIG. 2 is a flowchart illustrating a method of manufacturing ahigh-entropy alloy according to another embodiment of the presentdisclosure.

Referring to FIG. 2 , the present embodiment may include a preparationstep S30, a step S32 of forming an inert gas atmosphere after vacuum,and a melting step S34.

First, in the preparation step S30, all materials for manufacturing thehigh-entropy alloy may be put into the molten metal manufacturingequipment. Here, iron may be pure iron or pig iron.

Subsequently, in the step S32 of forming the inert gas atmosphere aftervacuum, the inert gas atmosphere may be formed while performing awashing operation in a chamber by repeatedly injecting inert gas aftercreating the vacuum atmosphere. Examples of the inert gas atmosphere mayinclude an argon (Ar) gas atmosphere.

Subsequently, in the melting step S34, the molten metal may bemanufactured by performing a melting operation at a predeterminedmelting temperature. For example, the melting temperature of the meltingstep S34 may be 1750° C. or less (e.g. 1650° C. or less), in detail,1200° C. to 1750° C. (e.g. 1400° C. to 1650° C., such as 1450° C. to1520° C.). However, the melting temperature of the melting step S34 maybe variously changed by the material forming the high-entropy alloy.

When the melting step S34 is completed, a tapping operation may beperformed at a predetermined tapping temperature (e.g., 1400 to 1600°C., such as 1500° C.), and then a process may be performed to have adesired shape (e.g., casting using a mold having a desired shape).However, the present disclosure is not limited thereto, and the tappingtemperature or the like may be variously changed.

According to the present embodiment, the melting step S34 is performedunder the inert gas atmosphere after vacuum, thus effectively preventingthe low melting point material from being lost by oxidation (e.g. theloss of aluminum). In particular, when the high-entropy alloy contains alarge amount of low melting point element (e.g. aluminum), themanufacturing method according to the present embodiment can moreeffectively prevent the loss of the low melting point material. Since itis unnecessary to consider the melting points of various materialsincluded in the high-entropy alloy, the manufacturing process can besimplified by a single melting step (S34). Thus, the high-entropy alloyhaving the desired composition can be easily manufactured through asimple process.

On the other hand, in conventional atmospheric casting having the singlemelting step in which the input sequence and the melting temperature arenot controlled, oxidation of the low melting point element (e.g.,aluminum) occurs during molten metal production, thereby causing thelarge loss of the low melting point element and deteriorating fluidity.In addition, when the molten metal is poured into the mold, oxide isintroduced, which may cause problems such as cracks in the cast product.

Hereinafter, the present disclosure will be described in more detailthrough experimental examples of the present disclosure. However, theexperimental examples of the present disclosure are merely illustrativeof the present disclosure, and the present disclosure is not limitedthereto.

EXAMPLE 1

A high entropy alloy having a composition according to Table 1 and achemical formula of Al₁₅Ni₁₅Cr₁₀(CuFe)₅₀Mn₁₀ was manufactured using themanufacturing method shown in FIG. 1 . In this case, the iron-containingmaterial used 4.67 at % carbon, 1.35 at % silicon, 0.27 at % manganese,0.11 at % phosphorus, 0.02 at % sulfur, 0.08 at % titanium, 0.01 at %vanadium, pig iron containing the remainder of iron, and additionalmanganese.

EXAMPLE 2

A high-entropy alloy was manufactured in the same manner as in Example1, except that it has the chemical formula ofAl₁₅Ni₅Cr₁₀Cu₁₀Fe₄₃Mn₁₅Si₂.

EXAMPLE 3

A high-entropy alloy was manufactured in the same manner as in Example1, except that it has the chemical formula ofAl₁₅Ni₅Cr₁₀Cu₁₀Fe₄₀Mn₁₃Si₂.

EXAMPLE 4

A high-entropy alloy was manufactured in the same manner as in Example1, except that it has the chemical formula of Al₁₅Ni₅Cr₁₀Cu₁₀Fe₄₀Mn₂₀.

EXAMPLE 5

A high-entropy alloy was manufactured in the same manner as in Example1, except that it has the chemical formula of Al₁₇Ni₃Cr₅Cu₁₅Fe₄₅Mn₁₅.

EXAMPLE 6

A high-entropy alloy was manufactured in the same manner as in Example1, except that it has the chemical formula of Al₁₃Ni₃Cr₆Cu₈Fe₅₅Mn₁₅.

COMPARATIVE EXAMPLE 1

A high entropy alloy having a composition according to Table 2 and achemical formula of Al₁₀Cr₂₀(CuFe)₆₀Mn₁₀ was manufactured by performinga single melting process in a vacuum.

COMPARATIVE EXAMPLE 2

A stainless steel (SUS316) was prepared.

COMPARATIVE EXAMPLE 3

A stainless steel (SUS304) was prepared.

COMPARATIVE EXAMPLE 4

Cast iron (GC250) was prepared.

COMPARATIVE EXAMPLE 5

A high-entropy alloy was manufactured in the same manner as inComparative Example 1, except that it was manufactured using pure ironand had the chemical formula of Al₁₅Cr₅(FeCuMn)₈₀.

COMPARATIVE EXAMPLE 6

A high-entropy alloy was manufactured in the same manner as inComparative Example 1, except that it was manufactured using pig ironand had the chemical formula of Al₁₅Cr₅(FeCuMn)₈₀.

<Composition Analysis>

A field emission scanning electron microscope (FE-SEM) photograph of thehigh-entropy alloy according to Example 1 is shown in FIG. 3 . Forreference, the compositions of Tables 1 and 2 were measured by an energydispersive spectrometry (EDS), and the content of each element wasexpressed in at %.

TABLE 1 Fe Cu Al Mn Cr Ni Iron-rich phase 25.51 16.01 17.69 6.65 10.1224.02 Copper-rich 6.04 64.31 10.75 6.37 0.88 11.65 phase

TABLE 2 Fe Cu Al Mn Cr Iron-rich phase 47.07 2.44 7.37 10.87 32.26Copper-rich 3.56 73.48 11.30 9.88 1.77 phase

Referring to Tables 1 and 2, it can be seen that the content of copperin the iron-rich phase in the high-entropy alloy according to Example 1containing nickel was 16.01 at %, which was significantly highercompared to Comparative Example 1 in which there was no nickel and thecontent of copper in the iron-rich phase in the high-entropy alloy was2.44 at %. Further, it can be seen that the content of iron in thecopper-rich phase in the high-entropy alloy according to Example 1containing nickel was 6.04 at %, which was higher compared toComparative Example 1 in which there was no nickel and the content ofiron in the copper-rich phase in the high-entropy alloy was 3.56 at %.That is, it can be seen that the copper content in the iron-rich phaseand the iron content in the copper-rich phase in the high-entropy alloyaccording to Example 1 containing nickel are increased. Thereby, it canbe seen that copper or iron is dissolved at a certain level or more inthe iron-rich phase and the copper-rich phase in the high-entropy alloyaccording to Example 1, so that a corrosion potential difference betweenthe iron-rich phase and the copper-rich phase may be reduced.

Further, referring to FIG. 3 , it can be seen that the iron-rich phaseand the copper-rich phase having different brightness are coexisted inthe high-entropy alloy according to Example 1. At this time, it can beseen that the iron-rich phase is present as the main phase and thecopper-rich phase is partially present.

<Salt Spray Test—Corrosion Resistance>

A salt spray test was performed on the high-entropy alloy according toExample 1 and Comparative Example 1. In the salt spray test, 5 wt % ofsodium chloride salt water was indirectly continuously sprayed with thenozzle pressure of 1.0 kg/cm², and the pH of 6.5 to 7.2 and thetemperature of 35° C. were maintained. FIG. 4(a) shows a photographbefore the salt spray test of the high-entropy alloy according toExample 1, FIG. 4(b) shows a photograph when maintained for 24 hourswhile spraying salt water, FIG. 4(c) shows a photograph when maintainedfor 72 hours while spraying salt water. In addition, FIG. 5 shows aphotograph when maintained for 24 hours while spraying salt water ontothe high-entropy alloy according to Comparative Example 1.

Referring to FIG. 4 , it can be seen that the high-entropy alloyaccording to Example 1 containing nickel was not significantly corrodedeven if salt spray was performed for a long time. On the other hand,referring to FIG. 5 , it can be seen that the high-entropy alloyaccording to Comparative Example 1 containing no nickel was greatlycorroded by salt spray and thus stained. Accordingly, it can be seenthat the alloy according to Example 1 including nickel has excellentcorrosion resistance.

<Potentiodynamic Polarization Test—Corrosion Resistance>

The high-entropy alloy according to Example 1 and the stainless steelaccording to Comparative Example 2 were subjected to a potentiodynamicpolarization test, and the results are shown in Table 3. In thepotentiodynamic polarization test, a 5 wt % sodium chloride aqueoussolution was used, Ag/AgCl was used as a reference electrode, and a scanrate was 0.33 (dE/dt).

TABLE 3 Comparative Example 1 Example 2 Corrosion Potential [V] −0.37−0.2 Dynamic Equilibrium Current −7.6 −7.6 Density [log (A/cm²)]

Referring to Table 3, it can be seen that the high-entropy alloyaccording to Example 1 has high corrosion resistance similar to that ofthe stainless steel according to Comparative Example 2 having highcorrosion resistance.

<Salt Spray Test—Corrosion Resistance>

A salt spray test was performed on the high-entropy alloy according toExamples 2 and 3. In the salt spray test, 5 wt % of sodium chloride saltwater was indirectly continuously sprayed with the nozzle pressure of1.0 kg/cm², and the pH of 6.5 to 7.2 and the temperature of 35° C. weremaintained. FIG. 6(a) shows a photograph before the salt spray test ofthe high-entropy alloy according to Example 2, and FIG. 6(b) shows aphotograph when maintained for 24 hours while spraying salt water. Inaddition, FIG. 7(a) shows a photograph before the salt spray test of thehigh-entropy alloy according to Example 3, and FIG. 7(b) shows aphotograph when maintained for 24 hours while spraying salt water.

Referring to FIGS. 6 and 7 , it can be seen that corrosion rarelyoccurred even when salt spray was performed on the high-entropy alloysaccording to Examples 2 and 3 having the nickel content of 5 at %. Forinstance, it can be seen that even when the content of nickel is not aslarge as 5 at %, excellent corrosion resistance can be obtained if thecomposition also contains silicon. It is expected that the corrosionresistance is improved by the formation of the oxide including silicontogether. When silicon is included and the content of nickel is reducedas described above, the material cost of a high-entropy alloy havingexcellent properties can be reduced by reducing the content of expensivenickel.

<Grindability>

The high entropy alloys according to Examples 1 and 4 and the stainlesssteel according to Comparative Example 3 were lathe-processed. Latheprocessing was performed under the conditions of the rotation speed of10000 rpm, the movement speed of 5000 feed, a tool of 6 pie, REM (0.5R),the depth of 0.7 mm (AP), and spacing (AE) of 70% of a tool diameter,and water-soluble cutting oil was used.

FIG. 8 shows a photograph of a sheet material that is formed byprocessing the high-entropy alloy according to Example 1. Referring toFIG. 8 , it can be seen that a cleanly processed sheet material may bemanufactured using the alloy according to Example 1. For example,processing is possible in this example without defects or damage even ata processing speed 4 times faster than that of stainless steel as inComparative Example 3. Thus, a processing time can be shortened whenapplied to an actual processed product. Further, in Example 1, there wasno breakage of the tool even at a high processing speed. Thereby, it canbe seen that it is possible to provide the cleanly processed sheetmaterial at a high processing speed.

Further, the processing speeds (grinding rates) and copper contents ofthe high-entropy alloys according to Examples 1 and 4, and the stainlesssteel according to Comparative Example 3 are shown in Table 4. At thistime, the processing speed per unit area was measured at a speed of 300rpm under a load of 800 g.

TABLE 4 Processing Speed Copper Content [s/mm²] [at %] Example 1 1.37 25Example 4 2.92 10 Comparative Example 3 3.33 —

Referring to Table 4, it can be seen that the processing speeds in thehigh-entropy alloys according to Examples 1 and 4 are significantlyhigher than the processing speed of the stainless steel according toComparative Example 3. For example, if the copper content is 25 at % ormore as in the high-entropy alloy according to Example 1, the processingspeed may be twice or more than the processing speed of the stainlesssteel according to Comparative Example 3. This is because thecopper-rich phase having excellent grindability or machinability wasmixed or interspersed with the iron-rich phase having high strength, inthe case of the high-entropy alloys according to Examples 1 and 4.

<Castability>

FIG. 9 shows the photograph of the Oldham ring having the thickness of1.7 mm manufactured using the high-entropy alloy according to Example 1.Further, FIGS. 10(a) and 10(b) show photographs taken as the result ofperforming 2 mm mesh channel evaluation on the high-entropy alloysaccording to Examples 5 and 6, and FIG. 11 shows a photograph taken asthe result of performing 2 mm mesh channel evaluation on the cast ironaccording to Comparative Example 4.

In addition, FIGS. 12(a) and 12(b) show photographs taken as the resultof performing wear resistance evaluation on the high-entropy alloysaccording to Examples 5 and 6, and FIGS. 13(a), 13(b), and 13(c) showphotographs taken as the result of performing wear resistance evaluationon the cast iron or high-entropy alloys according to ComparativeExamples 4, 5, and 6. Further, the hardness, 2 mm micro-channelfillability, wear-track width, and entropy of the high-entropy alloys orcast iron according to Examples 5 and 6 and Comparative Examples 4, 5and 6 were measured, and then the results are shown in Table 5. The wearresistance evaluation was performed using a ball made of aluminum oxide(Al₂O₃) under the conditions of a normal drag of 10 N, a rotationalspeed of 300 rpm, a rotational radius of 11.5 mm, and a time of 3000seconds.

TABLE 5 Hardness Fillability Wear-track Strain [Hv] [%] width [um]Entropy Example 5 0.025 374 81 2313-2373 1.48R Example 6 0.03 324 853059-3782 1.40R Comparative 0.036 — 77 1792-2051 — Example 4 Comparative0.015 391 68 1468-2409 1.49R Example 5 Comparative 0.039 238 791252-3007 1.49R Example 6

Referring to FIG. 9 , it can be seen that, when using the high-entropyalloy according to Example 1, the Oldham ring having the thickness of1.7 mm may be formed by precise processing.

Referring to FIGS. 10 and 11 and Table 5, it can be seen that the highentropy alloys according to Examples 5 and 6 have better castabilitythan the cast iron according to Comparative Example 4 having excellentcastability in the evaluation of the 2 mm mesh channel. This is becausethe high entropy alloys according to Examples 5 and 6 have high fluidityand have large wettability due to low surface energy, so that a micromesh channel mold may be stably filled. In particular, since coppercomponents included in the high entropy alloys according to Examples 5and 6 may contribute to improving wettability, Examples 5 and 6 may haveboth excellent fluidity and excellent wettability. On the other hand,the cast iron according to Comparative Example 4 has excellent fluiditybut poor wettability, so that it is difficult to manufacture a structurehaving micro-channels of 2 mm or less.

Referring to FIG. 12 and Table 5, it can be seen that the high-entropyalloys according to Examples 5 and 6 have excellent hardness, excellentwear resistance, and excellent castability. In particular, it can beseen that the high-entropy alloy according to Example 5 has veryexcellent hardness, wear resistance, and castability characteristics.Further, referring to FIG. 13(b) and Table 5, it can be seen that thehigh entropy alloy according to Comparative Example 5 showed excellenthardness and wear resistance, but had low fillability and uneven wear.Since the high-entropy alloy according to Comparative Example 5 has avery hard characteristic with a small strain, a large amount ofoxidation of aluminum occurs when manufactured by atmospheric casting,so that many bubbles and cracks may occur inside the cast product.Further, the cast iron according to Comparative Example 4 has relativelylow fillability and does not have high entropy. Furthermore, it can beseen that the high entropy alloy according to Comparative Example 6 haslow fillability, low hardness, and very irregular wear.

The above-described features, structures, effects, etc. are included inat least one embodiment of the present disclosure, and are notnecessarily limited to only one embodiment. Furthermore, the features,structures, effects, etc. illustrated in each embodiment may be combinedor modified for other embodiments by those of ordinary skill in the artto which the embodiments belong. Accordingly, the contents related tosuch combinations and modifications should be interpreted as beingincluded in the scope of the present disclosure.

What is claimed is:
 1. A high-entropy alloy having an iron-rich phaseand a copper-rich phase, wherein the high-entropy alloy comprises acommon complete solid solution metal that is completely solid-solved iniron and copper respectively.
 2. The high-entropy alloy of claim 1,wherein the common complete solid solution metal comprises nickel (Ni).3. The high-entropy alloy of claim 1, further comprising: a meltingpoint lowering element for lowering a melting point of the high-entropyalloy.
 4. The high-entropy alloy of claim 3, wherein the melting pointlowering element comprises at least one of carbon, silicon, phosphorus,and manganese.
 5. The high-entropy alloy of claim 1, wherein thehigh-entropy alloy further comprises at least one of aluminum,manganese, and chromium.
 6. The high-entropy alloy of claim 1, whereinthe high-entropy alloy comprises 15 to 80 at % iron, 1 to 30 at %copper, 1 to 20 at % nickel, 5 to 20 at % aluminum, 0 to 20 at %manganese, 0 to 15 at % chromium, 0 to 5 at % carbon, 0 to 2 at %silicon, 0 to 2 at % phosphorus, and other unavoidable impurities. 7.The high-entropy alloy of claim 1, wherein a content of the copper inthe iron-rich phase ranges from 5 to 30 at %.
 8. The high-entropy alloyof claim 1, wherein the iron-rich phase is contained in a larger volumeratio than the copper-rich phase to be present as a main phase, and thecopper-rich phase is partially present.
 9. A method for manufacturing ahigh-entropy alloy, comprising: an iron melting step of melting aniron-containing material including a melting point lowering element andiron to form a molten metal; a high melting point material melting stepof putting a high melting point element that has a melting point higherthan that of the iron-containing material into the molten metal, andmelting the high melting point element; a copper melting step of puttingcopper into the molten metal, and then melting the copper; and a lowmelting point material melting step of putting a low melting pointmaterial that has a melting point lower than that of the copper, andthen melting the low melting point material.
 10. The method of claim 9,wherein the iron-containing material comprises pig iron.
 11. The methodof claim 9, wherein the melting point lowering element comprises atleast one of carbon, silicon, phosphorus, and manganese.
 12. The methodof claim 9, wherein at least two of a first melting temperature of theiron melting step, a second melting temperature of the high meltingpoint material melting step, a third melting temperature of the coppermelting step, and a fourth melting temperature of the low melting pointmaterial melting step have different temperatures.
 13. The method ofclaim 12, wherein the second melting temperature is higher than thefirst melting temperature, the third melting temperature is lower thanthe second melting temperature, and the fourth melting temperature islower than the third melting temperature.
 14. The method of claim 9,wherein the high-entropy alloy comprises a common complete solidsolution metal that is completely solid-solved in iron and copperrespectively.
 15. The method of claim 9, wherein the high melting pointmaterial comprises at least one of nickel and chromium.
 16. The methodof claim 9, wherein the low melting point material comprises aluminum.17. The method of claim 16, wherein, in the low melting point materialmelting step, aluminum ingot is pushed into a bottom portion of themolten metal to be melted.
 18. A method for manufacturing a high-entropyalloy, comprising: a basic step of putting a plurality of materialsincluding iron, copper, and a common complete solid solution metal thatis completely solid-solved in iron and copper respectively; a step offorming inert gas atmosphere after vacuum; and a melting step of meltingthe plurality of materials.
 19. The method of claim 18, wherein theplurality of materials further comprise at least one of carbon, silicon,phosphorus, aluminum, manganese, and chromium, and the common completesolid solution metal comprises nickel.
 20. The method of claim 18,wherein the iron comprises pig iron or pure iron.